Comparative and evolutionary studies suggest that the tectopulvinar system is one of the most ancient components of the ascending pathways to the telencephalon and is vital to the process of motion detection. Improved understanding of this system may clarify the processing of visual information for detection of motion and direction in nonmammals and thus the evolution of such processing in mammals. The tectopulvinar system may be viewed as a series of visual information processing stages: Stage I processing-Retina: presumably simple On/Off cells with extremely small receptive fields; Stage II processing-Tectum: high speed motion detection by tectal neurons of the stratum griseum central (SGC) of birds and the lower stratum griseum superficiale (SGSL) of mammals in direct receipt of retinal inputs upon their unique "bottlebrush" dendritic endings; Stage III processing- Thalamus: global direction detection by specific thalamic neurons of the nucleus rotundus of birds and the nucleus inferior pulvinar in mammals; and Stage IV processing - Telencephalon: processing of directionality and possible restoration of retinotopy. This proposal is to study the substrate of motion detection and evolution of the tectopulvinar system in chicks, pigeons and squirrels, using immunohistochemistry, confocal microscopy, intracellular cell filling and physiological techniques to- answer the following questions: Studies of Stage II - Are motion detection cells of SGC/SGSL influenced by nonretinal inputs? We will examine the inputs from the nucleus isthmi and parabigemini, each the source of a major cholinergic projection upon the layer of bottlebrush dendritic endings in birds and mammals, respectively and of various telencephalic inputs. What is the topography of reciprocal connections of the tectum and the isthmi? Do cholinergic inputs influence the responses of bottlebrush dendritic endings to retinal stimulation? Studies of Stage III - How is directionality generated from motion by thalamic neurons? Specifically, how do SGC/SGSL neuronal axons terminate in the rotundus/inferior pulvinar? What is the three-dimensional morphology of rotundus/inferior pulvinar neurons in birds and mammals? Are there divisions in the inferior pulvinar of the squirrel that correspond to the divisions in the rotundus of birds? What are the physiological ro erties of the squirrel inferior pulvinar?